The inner surface of a pneumatic tire may include an elastomeric composition designed to prevent or retard the permeation of air from the inner air chamber of the tire. This elastomeric composition is often referred to as an innerliner. Rubbers, such as butyl and halobutyl rubber, which are relatively impermeable to air, are often used as the primary rubber component in innerliners.
The innerliner is generally a relatively thin sheet of elastomer that is formulated with compounding additives and a curing system. This thin sheet is laminated to the inner surface of a tire carcass layer of an uncured tire as the tire is formed on a tire building drum. Final cure of the composite structure produces a tire having a cured innerliner adhered to the carcass.
Properties that are desirable for innerliners include good resistance to air permeation, flex resistance, and adhesion to the tire carcass. It is also desirable that the green innerliner have sufficient green strength to prevent damage (e.g., tears) during tire construction. Low permeability to air is generally achieved through the use of a high mechanical Tg polymer, such as butyl rubber or a halobutyl rubber. The high Tg polymer may be blended with other elastomers such as SBR or natural rubber. Flex resistance and tensile strength depends, to some degree, on modulus.
While the strength of rubber compositions has historically been improved through the use of reinforcing carbon black, recent developments have found that layered minerals, such as layered silicates (also referred to as clays), can be used as filler materials within innerliner rubber compositions to improve resistance to air permeation and allow for the use of thinner gauge innerliners. For example, a portion of the carbon black volume within an innerliner composition can be replaced with the layered silicate to achieve these advantageous results.
While thinner gauge innerliners have proven to be advantageous, they present manufacturing challenges because green strength is diminished at thinner gauges, and therefore tears and other damage to the innerliner can be problematic at these thinner gauges.
With continued demands on innerliners and production of tires using thinner innerliners, there is a continued need to improve upon this area of technology.